Corrosion inhibitors

ABSTRACT

Corrosivity of non-aqueous solutions of copper ions useful in olefin separation processes is greatly reduced by addition of from about 0.5 to about 15 percent by weight of a metal salt of an ortho-hydroxy aromatic carboxylic acid to such solutions.

United States Patent [151 3,656,886 Blytas [4 Apr. 18, 1972 [54] CORROSION INHIBITORS 2,182,612 12/1939 Eaton ..252/389 x 2,197,832 4/1940 Reiff .....252/389 X [721 Invenm Kensmgmn Cahf' 2,258,591 10/1941 Moser et al. .....252/3s9 x [73] Assignee: Shell Oil Company, New York, NY. 2,311,931 1943 COOK -25 /389 X 7 2,714,092 7/1955 Culnane et ,....252/389 X 1 F1199! 12, 1979 3,349,043 10/1967 Manning et al. ..252/396 x l A l. N 2,439 PP 0 Primary Examiner-Moms O. W0lk Assistant Examiner-Joseph T. Zatarga [52] US. Cl ..2l/2.5, 252/389, 252/396 Attorney-John H, Colvin and Raymond Owyang [51] Int. Cl. ..C23I 11/10 [58] Field of Search ..2l/2.5; 260/6815 C, 666.5; [57] ABSTRACT Corros1v1ty of non'aqueous solutions of copper ions useful in olefin separation processes is greatly reduced by addition of [56] References Cned from about 0.5 to about 15 percent by weight of a metal salt of UNITED STATES PATENTS an ortho-hydroxy aromatic carboxylic acid to such solutions. l,940,04l 12/1933 Avis.. ..252/389 X 4 Claims, No Drawings CORROSION INHIBITORS BACKGROUND OF THE INVENTION the aqueous medium to enhance the disproportionation of cuprous ion to non-complexing species, cupric ion and metallic copper, by forming the relatively more stableaquo-cupric complex, e.g., Cu(l-l O),, Non-aqueous media, such as alcohols and amines as proposed by U.S. Pat. No. 2,376,239, is- 1 sued May 15, 1945 to Evans et al., ethylene glycol acetonitrile, as proposed by U.S. Pat. No. 2,275,135, issued March 3, 1942 to Fasce, the xylenes, and propionitrile as proposed by U.S. Pat. No. 3,401,112, issued Sept. 10, 1968 to Dunlop et al., while being more efficient for olefin separation,

have the disadvantage of being undesirably more corrosive to the metals of which parts of practical scale separation apparatus are constructed, particularly ferrous metals such as iron and carbon steel. Such corrosion is apparently due to the small amounts of cupric ions inherent in cuprous salt olefin separation systems. Corrosion has been found in these systems even when the apparatus used is scrupulously decontaminated prior to use and the solutions are carefully purified.

STATEMENT OF THE INVENTION It has now been found that the corrosive nature toward ferrous metals of solutions of copper ions as used in olefin separation process is reduced to a substantial extent by addi-' DETAILED DESCRIPTION OF THE INVENTION Preferred corrosion inhibitors according to the invention are metal salts of the alkyl substituted and unsubstituted salicyclic acids such as metal salts of salicylic acid, ethyl salicylic acid, isopropyl salicylic acid, n-butyl salicylic acid, isobutyl salicylic acid, tert-butyl salicylic acid, hexyl salicylic acid, diethyl salicylic acid, diisopropyl salicylic acid, ditertiarybutyl salicylic acid, diisobutyl salicylic acid, ditertiary-pentyl salicylic acid, tri-ethyl salicylic acid, and the like. Especially preferred are metal salts of salicylic acid having at least one but not more than two alkyl substituents each of from about two to about six carbon atoms. Metal salts of dialkyl substituted salicylic acids having from two to six carbons per alkyl substituent are most preferred.

As metal ions in the metal salt inhibitors according to the invention may be used monovalent metal ions such as ions of the alkali metals and transition metals, for example, Sodium 1, Potassium I, Lithium 1, Copper 1, and Silver 1,.

Cuprous (Copper 1) is a preferred metal for inhibitor salts according to the invention. Most preferred as inhibitor salts are the cuprous salts of dialkyl substituted salicyclic acids having from two to six carbon atoms per substituent, such as cuprous diisopropyl salicylate, cuprous ditertiary-butyl salicylate, and cuprous ditertiary-pentyl .salicylate. Mixtures of inhibitor salts may be employed.

The inhibitors according to the invention may be used to prevent corrosion in any non-aqueous solvented cuprous ion olefin separation process. They are especially useful in preventing corrosion in processes which use propionitrile as cuprous salt solvent and which contain a minimum of about 5 percent by weight of cuprous copper such as that described in U-.S.Pat.No. 3,401,112.

The amount of inhibitor salt added to olefin separation systems may vary widely. Generally suitable for additions of inhibitor salt equivalent to from about 1 to about 20 percent by mole of the cuprous salt present in such cuprous olefin separation systems. When the preferred alkyl substituted metal salicylates are employed, additions of from about 2 percent to about 15 .percent by mole (based on the total-moles of cuprous ion present) are preferred. Especially preferred are additions of from about 3 percent to about 10 percent by mole based on the total moles of cuprous ion present.

EXAMPLE I A sample of mild carbon steel was prepared and immersed in a non-aqueous solution of cuprous salt suitable for use in olefin separation processes. The solution contained 12 percent by weight cuprous ion, supplied as triiluoroacetate and about 1.5 percent by weight of cupric ion.

Propionitrile was the solvent. Corrosion rate of the steel samples was determined by weight loss of the sample after a measured time interval. The sample was held at C during the test. Without the addition of inhibitor, the corrosion rate as 34 m.p.y. A second sample was immersed in a similar cuprous trifluoroacetate solution in propionitrile to which had been added 5 percent by weight of an inhibitor according to the invention, cuprous ditertiary-butyl salicylate. This propionitrile solution contained 12 percent by weight of cuprous ion and 1.3 percent by weight of cupric ion. The corrosion rate at 100 C. was 3m.p.y. Example 11 Corrosion rates, with and without inhibitor, were determined on mild carbon steel samples at C in a manner similar to Example I in cuprous trifluoroacetate solution in xylene. In the absence of inhibitor the corrosion rate was 70 m.p.y. When 6 percent by weight of cuprous ditertiary-butyl salicylate was added the corrosion rate was 10 m.p.y. The concentration of cuprous ion present in the solution as cuprous trifluoroacetate was 20 percent by weight and the cupric ion concentration was 3 percent by weight.

1 claim as my invention:

1. The method of inhibiting corrosion of ferrous metals by nonaqueous solutions of copper ions which consists essentially of adding to such solutions cuprous carboxylic salts of alkyl ring-substituted salicylic acids having at least one but not more than two alkyl substituents each of from two to six carbon atoms.

2. The method in accordance with claim 1 wherein the nonaqueous solution of copper ions is a propionitrile solution which contains a minimum of about 5 percent by weight of cuprous copper.

3. The method in accordance with claim 1 wherein said metal salts are selected from the group consisting of cuprous salts of salicylic acids having two alkyl substituents each of from about two to about six carbon atoms and such salt is added in amount equivalent to from about 1 to about 20 percent by mole of the copper ion present.

4. The process in accordance with claim 1 wherein said metal salt is cuprous ditertiary-butyl salicylate.

CUPI'OUS 

2. The method in accordance with claim 1 wherein the nonaqueous solution of copper ions is a propionitrile solution which contains a minimum of about 5 percent by weight of cuprous copper.
 3. The method in accordAnce with claim 1 wherein said metal salts are selected from the group consisting of cuprous salts of salicylic acids having two alkyl substituents each of from about two to about six carbon atoms and such salt is added in amount equivalent to from about 1 to about 20 percent by mole of the copper ion present.
 4. The process in accordance with claim 1 wherein said metal salt is cuprous ditertiary-butyl salicylate. 